Abstract
Cyanobacteria are highly versatile organisms in spite of their small size; they represent the smallest photosynthetic units on Earth, and gave rise to algae and plants. Cyanobacteria are globally widespread in terrestrial and aquatic environments, including the large oceans. In recent years they have attracted attention because of their high evolutionary importance, their developmental complexity, their unexpected pivotal ecological significance in global biogeochemical cycles and their production of a large number of secondary metabolites, many with great biotechnological potential. In this overview, focus is on the role of cyanobacteria in the origin and evolution of algae and plants, and on mechanisms in contemporary cyanobacterial-plant symbioses (Gunnera and Azolla) that may represent ‘blue-prints’ of those that some 2.1 billion years ago became the first chloroplasts.
